Monolithic, super heat-insulating, organic aerogel composition preparation method, said composition, and the use thereof
The invention relates to a process for preparing a gelled, dried composition forming a monolithic aerogel with a heat conductivity of less than or equal to 40 mW·m −1 ·K −1 and derived from a resin of polyhydroxybenzene(s) and formaldehyde(s), to this aerogel composition and to the use thereof. This process comprises: a) polymerization in an aqueous solvent of said polyhydroxybenzene(s) and formaldehyde(s) in the presence of an acidic or basic catalyst, to obtain a solution based on the resin, b) gelation of the solution obtained in a) to obtain a gel of the resin, and c) drying of the gel to obtain a dried gel. According to the invention, step a) is performed in the presence of a cationic polyelectrolyte dissolved in this solvent, and the process also comprises a step d) of heat treatment under inert gas of the dried gel obtained in step c) at temperatures of between 150° C. and 500° C. to obtain the non-pyrolyzed aerogel whose heat conductivity is substantially unchanged, even after exposure to a humid atmosphere.
1. A process for preparing a gelled, dried and non-pyrolyzed composition forming an organic monolithic aerogel with a heat conductivity of less than or equal to 40 mW·m−1·K−1, the composition being at least partly derived from a resin obtained by polycondensation of at least one polyhydroxybenzene R and at least one formaldehyde F, the process comprising:
a) polymerizing the at least one polyhydroxyhenzene R and the at least one formaldehyde in an aqueous solvent W in the presence of an acidic or basic catalyst, to obtain a solution based on the resin;
b) gelling the solution to obtain a gel of the resin; and
c) drying the gel to obtain a dried gel,
wherein:
the polymerizing a) is performed in the presence of at least one water-soluble cationic polyelectrolyte P dissolved in aqueous solvent W; and
the process further comprises a step d) of heat treating the dried gel under an inert gas at temperatures of between 150° C. and 500° C. to obtain the gelled, dried and non-pyrolyzed composition.
2. The process of claim 1 , wherein the dried gel has a core and a surface layer which both comprise oxygenated groups, which are only partially carbonized in the heat treating, such that the gelled, dried and non-pyrolyzed composition comprises several said oxygenated groups which are intact in the core and in the surface layer.
3. The process of claim 2 , wherein the gelled, dried and non-pyrolyzed composition comprises hydroxyl groups, formaldehyde groups, or both, as the oxygenated groups.
4. The process of claim 1 , wherein the heating treating d) comprises at least one temperature increase followed by at least one heat stabilization stage, and ends with gradual cooling to a temperature of between 15 and 30° C.
5. The process of claim 4 , wherein the heat treating d) comprises:
a first temperature increase at a rate of between 1 and 5° C./minute up to an intermediate temperature of between 100 and 200° C., followed by a first stabilization stage at the intermediate temperature lasting between 5 and 30 minutes;
a second temperature increase at a rate of between 2 and 10° C./minute up to a final temperature of between 240 and 460° C., followed by a second stabilization stage at the final temperature lasting between 1 hour and 3 hours; and then
said gradual cooling for a time of at least 45 minutes to a temperature of between 20 and 25° C.
6. The process of claim 1 , wherein the at least one water-soluble cationic polyelectrolyte P used during the polymerizing a) is present in the gelled, dried and non-pyrolyzed composition at a mass fraction of between 0.2% and 2% relative to a total mass of the composition.
7. The process of claim 1 , wherein the at least one water-soluble cationic polyelectrolyte P is an organic polymer selected from the group consisting of an organic quaternary ammonium salt, a poly(vinylpyridine chloride), a poly(ethyleneimine), a poly(vinylpyridine), a poly(allylamine hydrochloride), a poly(trimethylammonium chloride ethylmethacrylate), a poly(acrylamide-co-dimethylammonium chloride) and mixtures thereof.
8. The process of claim 1 , wherein the polymerizing a) occurs at a temperature of between 15 and 30° C., by dissolving the at least one polyhydroxybenzene R and the at least one cationic polyelectrolyte P in the aqueous solvent W, followed by adding to a solution obtained the at least one formaldehyde F and the acidic or basic catalyst.
9. The process of claim 1 , wherein, before the gelling b), at least one filler that is capable of absorbing infrared radiation is added to the solution.
10. The process of claim 1 , wherein the drying c) is performed by oven drying, the drying c) being performed without solvent exchange and without drying with a supercritical fluid.